The present invention relates to a constant velocity universal joint of the tripod type having an outer joint part with three axially extending, circumferentially distributed longitudinal recesses with two circumferentially opposed tracks each. The tracks have surfaces which are grooved so as to have the shape of a circular cylindrical portion. An inner joint part includes three radial circumferentially distributed arms each engaging one of the longitudinal recesses and carrying roller assemblies with roller carriers and roller elements. The roller elements have running faces in the shape of a spherical portion and which are axially guided so as to roll on the tracks in the longitudinal recesses of the outer joint part. The roller carriers are guided on the arms so as to be pivotable and longitudinally movable relative to the respective arm axis. The roller elements are coaxially supported on the roller carriers so as to be rotatable optionally by roller or needle bearings. The roller assemblies, which include the roller carriers and roller elements, prevent the assemblies from tilting relative to the outer joint part, and are supported on the base of the recesses and on longitudinally extending guiding shoulder faces of the outer joint part which radially inwardly adjoin the tracks. The axes of the surfaces, in the shape of a circular cylindrical portion, of the tracks in each recess substantially coincide with the center of the roller element surface, in the shape of a spherical portion, with the track radius optionally being slightly greater than the radius of the roller surface. The cooperation of the surfaces thus does not generate any resistance against tilting around all axes, which means that the additional means for guiding and supporting the roller assembly are essential to prevent it from tilting.
Relevant joints are shown in EP 0 426 186 A1. In these joints, the radially inner end of the roller carrier is provided with a collar which serves to Support the roller assembly relative to the outer joint part. In EP 0 298 249 B1, the radially outer end of the roller carrier may also be provided with a collar which serves to support the roller assembly relative to the outer joint part. This type of support ensures the substantially rolling movement of the roller element relative to the tracks in the outer joint part, with the axis of the roller element always being parallel thereto. However, if viewed in a section extending perpendicularly to the axis of the outer joint part, a slight inclination of the roller axis relative to the arm axis is said to be possible under torque loading in order to ensure that the track surface is loaded uniformly by the roller element. On the other hand, any tilting of the roller axis relative to the axis of the outer joint part and thus relative to the tracks, if viewed in a longitudinal section through the joint, is to be avoided by the shoulder to maintain, at all times, a purely rolling movement when the joint rotates in the articulated condition.
A typical feature of the joint of the above-mentioned type consists in that the roller carrier should not be held on the tripod arm so as to be able to rotate because the relative movement between the roller element and arm is to take place in the bearing, between the roller element and roller carrier provided for that purpose. However, as a result of the contact between the shoulder at the roller carrier and the supporting counter-shoulder at the tracks, the roller carrier is forced to carry out a rotational movement which leads to sliding friction either between the arm and bore of the roller carrier or between the roller carrier and the outer joint part in the region of the supporting annular shoulder.
DE 28 31 044 A1, proposes joints of the above-mentioned type where only the roller element is in contact with the tracks. A tilting movement of the roller element relative to the tracks can only be prevented by the roller elements including running faces which deviate from the spherical shape and which are either crowned or roof-shaped in section. Producing corresponding non-spherical surfaces at the roller elements and the respective rolling faces at the tracks constitutes a problem. In consequence, a uniform load application along the contact line between the roller element and track is difficult to achieve. Any tilting of the roller elements relative to the outer joint part, when the inner joint part is in an articulated position relative to the outer joint part, can only be prevented by a form-fitting contact between the roller elements and tracks which has the tendency of leading to the entire roller element tilting in the tracks and thus to a jamming effect and increased loads at the upper and lower annular edges of the roller elements.
DE 37 16 962 C2, proposes a tripod joint of a similar kind, where the bearing is arranged differently and thus, instead of a non-rotating bearing carrier, an inner roller is provided which rotates relative to the arm. The roller elements have the shape as described in the previous publication so that the problems in respect of roller guidance are the same. In this case, too, the roller elements are guided in the tracks as a result of a complete form-fitting contact between the two components in the cross-section which leads to jamming of the roller elements and thus increased edge loads when the inner joint part is articulated relative to the outer joint part.
DE 31 03 172 A1, illustrates similar joints where, as in the initially mentioned publication, the roller assembly is supported relative to the outer joint part via an enlarged radially inner collar at the roller carrier or via an intermediate ring between the roller element and the roller carrier. With the first mentioned embodiment, the disadvantages are the same as those mentioned above. The second mentioned embodiment leads to a sliding friction at the intermediate ring relative to the roller carrier or relative to the shoulder faces and the roller element.